We must not and cannot admit that because the Bible itself says there is another authority to be obeyed:
2Thes:2:15: Therefore, brethren, stand fast: and hold the traditions, which you have learned, whether by word or by our epistle.
I would first point out that the context of the passage is teachings about salvation that had been handed down, but I'll be flexible.
First, the passage says these teachings had already been passed down by word prior to the writing of the letter to the Thessalonians. It says some of them had been delivered face-to-face (by word) and some by epistle.
It is obvious that none of us living today were present to hear those face to face sermons of Paul. But it is comforting to know that very early Paul affirms the authority of his epistles, and that some had already been written and sent out.
There is no acknowledgement that anyone other than the "our" mentioned in the passage could be the source of any teaching that was to be followed. Therefore, it had to be a teaching of Paul.
And we have the other necessary teachings of Paul preserved in his many other letters.